1. Related Art
Rapid Prototypying and Manufacturing (RP&M) is the name given to a field of technologies that can be used to form three-dimensional objects rapidly and automatically from three-dimensional computer data representing the objects. RP&M can be considered to include three classes of technologies: (1) Stereolithography; (2) Laminated Object Manufacturing; and (3) Selective Deposition Modeling.
The stereolithography class of technologies create three-dimensional objects based on the successive formation of layers of a fluid-like medium adjacent to previously formed layers of medium and the selective solidification of those layers according to cross-sectional data representing successive slices of the three-dimensional object in order to form and adhere laminae. One specific stereolithography technology is known simply as stereolithography and uses a liquid medium which is selectively solidified by exposing it to prescribed stimulation. The liquid medium is typically a photopolymer and the prescribed stimulation is typically visible or ultraviolet electromagnetic radiation. Liquid-based stereolithography is disclosed in various patents, applications, and publications of which a number are briefly described in the Related Applications section hereinafter. Another stereolithography technology is known as Selective Laser Sintering (SLS). SLS is based on the selective solidification of layers of a powdered medium by exposing the layers to infrared electromagnetic radiation to sinter or fuse the particles. SLS is described in U.S. Pat. No. 4,863,538 issued Sep. 5, 1989 to Deckard. A third technology is known as Three-dimensional Printing (3DP). 3DP is based on the selective solidification of layers of a powdered medium which are solidified by the selective deposition of a binder thereon. 3DP is described in U.S. Pat. No. 5,204,055 issued Apr. 20, 1993 to Sachs. A third technique is called Multijet Modeling, MJM, and involves the selective deposition of droplets of material from multiple ink jet orifices to speed the building process. MJM is described in PCT Publication Nos. WO 97-11835 published Apr. 3, 1997 naming Leyden as an inventor and WO 97-11837 published Apr. 3, 1997 naming Earl as an inventor (both assigned to 3D Systems, Inc. as is the instant application). Another patent describing Selective Deposition Modeling is U.S. Pat. No. 5,943,235 entitled "Method and Apparatus for Data Manipulation and System Control in a Selective Deposition Modeling System" which is assigned to the assignee of the present invention and which is incorporated by reference herein in pertinent pat.
Laminated Object Manufacturing, LOM, techniques involve the formation of three-dimensional objects by the stacking, adhering, and selective cutting of sheets of material, in a selected order, according to the cross-sectional data representing the three-dimensional object to be formed. LOM is described in U.S. Pat. Nos. 4,752,352 issued Jun. 21, 1998 to Feygin; and 5,015,312 issued May 14, 1991 to Kinzie, and in PCT Publication No. WO 95-18009 published Jul. 6, 1995 naming Morita as an inventor.
Selective Deposition Modeling, SDM, involves the build-up of three-dimensional objects by selectively depositing solidifiable material on a lamina-by-lamina basis according to cross-sectional data representing slices of the three-dimensional object. One such technique is called Fused Deposition Modeling, FDM, and involves the extrusion of streams of heated, flowable material which solidify as they are dispensed onto the previously formed laminae of the object. An example FDM process is described in U.S. Pat. No. 5,121,329 issued Jun. 9, 1992 to Crump. Another technique is called Ballistic Particle Manufacturing, BPM, which uses a 5-axis, ink-jet dispenser to direct particles of a material onto previously solidified layers of the object. Example BPM processes are described in PCT publication numbers WO 96-12607 published May 2, 1996 listing Brown as an inventor; WO 96-12608 published May 2, 1996 listing Brown as an inventor; WO 96-12609 published May 2, 1996 listing Menhennett as an inventor; and WO 96-12610 published May 2, 1996 listing Menhennett as an inventor, all assigned to BPM Technology, Inc.
Preferred embodiments of the present invention are primarily directed to Selective Deposition Modeling methods, systems, and apparatuses. Specifically, embodiments of the present invention involve the temperature control for controlling the solidification of the solidifiable material and, preferably, reducing the time required to build a three-dimensional object. Various solidifiable materials (e.g., polymer waxes and thermopolymer waxes) may be used in Selective Deposition Modeling processes to form a three-dimensional object. The material will preferably melt at a temperature above its melting point temperature to allow selective deposition and rapidly solidify at a temperature below its freezing point temperature to form part of a three-dimensional build structure. The melting point and freezing point temperatures are inherent properties of the selected solidifiable material.
The temperature of the environment in which the material solidifies may be an ambient temperature or it may be artificially produced. The temperature must be low enough, relative to the melting point temperature of the material, to cause the material to solidify or freeze at a particular rate. However, if the temperature is too low, the solidified material may experience built in stresses or brittleness.
A technique used in Selective Deposition Modeling systems previously manufactured by 3D Systems Inc. (the Assignee of the present invention) for controlling the build temperature employed cooling fans mounted near the dispenser that dispenses the solidifiable material. The fans are operated at a constant rate through the building process to cool the solidifiable material by blowing air onto the solidifiable material during the formation of the three-dimensional object. Specifically, the fans generally cool each layer or lamina substantially instantaneously upon dispensation and continue to blow air on each layer or lamina after dispensation. Hence, some regions of the three-dimensional object can become colder than other regions. If the different regions are allowed to remain at different temperatures, the three-dimensional object may experience a differential amount of shrinkage as it is cooled. This differential in shrinkage could lead to the development of stresses within the object and associated distortions of the object.
Building an object on a layer-by-layer basis can take a considerable amount of time. The amount of time required to build an object is related to several factors, such as the type of solidiflable material used to build the object and the dispensing rate of the solidifiable material. The dispensing rate of the solidfiable material is related, at least in part, to the freezing point of the solidifiable material.
When dispensing layer after layer of solidifiable material, the dispenser may be required to wait between layers, to allow the most recently formed layer to sufficiently freeze before dispensing the next layer. For low freezing point temperatures, the dispenser may have to wait a long time until the previous drop freezes. For example, assume that one solidifiable material has a freezing point of 60.degree. C. and another solidifiable material has a freezing point of 50.degree. C. Assuming both materials have the same dispensing temperature (and other parameters, such as heat conductivity, drop volume, support temperature, etc. are the same), the material with the freezing point of 50.degree. C. will take longer to solidify than the material with the freezing point of 60.degree. C. Hence, the time it takes to build a three-dimensional object would be longer for the solidfiable material with a freezing point of 50.degree. C. than for the solidifiable material with a freezing point of 60.degree. C.
Other factors may also affect the time it takes for each drop to solidify or freeze (e.g., the insulating properties of the solidfiable material and/or the ambient temperature). The past techniques tended to pre-set the dispensing rate based either on the inherent properties of a solidifiable material or on experimental data. Such pre-setting is generally inefficient because it does not consider the build-time state (i.e., temperature) of the object. The pre-setting scenario typically produces a constant dispensing rate and creates an open loop system that lacks the benefit of feedback information (i.e., current temperature of the object). Without feedback, the dispensing rate may not be increased (or decreased) based on the current temperature of the object. Thus, the use of a constant dispensing rate can prolong the time it takes to build a three-dimensional object.